The purpose of this project is to provide consultation on statistical and epidemiological methodology in the design, interpretation, and evaluation of clinical trials of diagnosis, treatment, and prevention of cancer, and other studies requiring this kind of expertise. For some studies the Section provides full statistical support, including development of detailed study plans, assistance in the design of appropriate study forms, supervision of randomization (for trials) and collection, processing, and editing of data, performance of interim analyses during the progress of the study, preparation of progress reports, final analysis of study data, and collaboration in the preparation of scientific papers. During the past year the Section has continued to collaborate extensively on the design and implementation of the Community Intervention Trial for Smoking Cessation: key activities during this year were the baseline survey and the randomization of communities. The Section has continued to provide full statistical support for the randomized clinical trials of treatment conducted by the Brain Tumor Cooperative Group. Other important activities under this project include (1) multiple regression analyses of risk factors for breast cancer, using data from three major national studies; (2) studies of selenium pharmacokinetics (ZO1 CN 00107-06 BB) applicable to possible prevention trials; (3) investigations to estimate population consumption of foods thought to be protective or harmful to cancer risk: (4) collaboration on a study of food purchasing behavior and consumer nutrition education; and (5) collaboration on workshops and planning sessions concerning the role of diet in gastric cancer and the design of intervention trials for this disease, including the role of intermediate endpoints.